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32-Bit Barrel Shifter

32-Bit Barrel Shifter. Carry In / Carry Out. -Carry in only used in RRX (rotate right extended) operations -Carry out always computed, even though not needed in rotate operations. Carry Out Logic: Two Options. Separate logic computes Cout early using input and shift amount. Pros:

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32-Bit Barrel Shifter

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  1. 32-Bit Barrel Shifter Carry In / Carry Out -Carry in only used in RRX (rotate right extended) operations -Carry out always computed, even though not needed in rotate operations

  2. Carry Out Logic: Two Options • Separate logic computes Cout early using input and shift amount Pros: -Cout signal ready much earlier, no need for propagation -Simpler bit shifter designs Cons: -Many more gates needed

  3. Carry Out Logic: Two Options • Individual bit shifters compute and propagate Cout signal Pros: -Simpler overall design -Fewer logic gates Cons: -Takes longer for Cout to be ready (propagation delay) -More complicated bit shifters

  4. Conclusion • Went ahead and implemented Cout logic in the bit shifters -Don’t really need the signal to be ready any earlier than the rest of the shifter output, especially not at the addition gate cost -Each shifter computes Cout for its own shift amount and passes it on, or leaves Cout alone if it is disabled

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